Same deal. We are located in Northern Virginia. Since the middle of June we have been experiencing the same exact symptoms as yourself. - can still get normal download speeds for the most part but have insanely high "world" latency and low "home" latency which renders WoW unplayable.
Tech support has not been helpful. Nothing in our setup has changed at all. Wondering if it's even worthwhile to have them send a tech out since it's likely (as you suggested) something Verizon is doing. Only other thought was that perhaps it was related to a tornado-producing storm we had that week - not sure where you are located.